In the shallow waters off the island of Mersea in Essex lies a little known English delicacy.

Colchester Native oysters were, legend has it, described by the Romans as the only good thing to come out of Britain. Two thousand years on, the slow-growing molluscs with their distinctive flat shells are now finding favour with an increasingly open-minded local audience as well as luxury goods purveyors as far afield as Dubai.

A growing appetite for oysters from browsers at the stalls of farmers' markets to business travellers in airport champagne bars has helped this niche British industry buck the recession.

For Richard Haward, whose family have been cultivating oysters off Mersea since the 18th century, it is a breakthrough that was always waiting to happen.

"People talk about organic and now increasingly they talk about natural foods. Wild oysters are the ultimate natural produce," he explains over the sound of purifying water trickling through pallets piled high in his shed.

They are about as essential to cash-strapped consumers as truffle oil in a recession, but Haward's oysters have enjoyed rising sales during the downturn.

"There are more people buying them and people are being more adventurous with food because they are going abroad more," he explains. "Celebrity chef endorsement also helps."

He points to a stack of tightly packed wooden boxes destined for Rye in East Sussex and another pile that will end up in airport bars. Haward's oysters are also sold in Belgium, where they are savoured by connoisseurs as "Les Colchesters", the far east and even the high-class restaurants of Paris.

But to say business is booming would be to misunderstand the nature of Colchester Natives.

Fattened over four or five years by food flowing from the surrounding Mersea marshlands, these filter feeders can only tolerate so much competition. They need space and time and under a 19th-century law can only be sold in months with an 'r' in them – September to April. They are the antithesis of fast food, something that has earned them a coveted place in the Slow Food movement's Ark of Taste.

It is also reflected in their price – £20 will buy you a mere dozen of Haward's Colchester Natives but for the same price you get twice as many of his easier to produce non-native Gigas, or rock, oysters.

The native Essex oysters are plumper and, for Haward, something best enjoyed pure. He grimaces when asked about Tabasco and lemon juice.

They are a labour of love too. The days of sailing boats and men toiling by hand to haul trays of oysters from Mersea's underwater creeks are gone. But beyond engine-powered boats and winches little has changed, as Haward's gnarled hands testify. Once dredged up, the oysters are still sorted by hand on board his 62-year-old wooden boat. The smaller ones are thrown back to fatten for longer, the keepers are scraped clean. The oysters are wild but Haward and his team of seven workers give nature a helping hand by removing pests such as starfish and by moving their stocks to seabeds with the best food. The days are long, mostly lonely and often cold, especially ahead of the Christmas rush.

It is a world away from the life Haward's father imagined for his son as the teenager left grammar school in the 1960s.

"My father wanted me to get a proper job where you work nine to five and retire at 60 and get a pension. The [oyster] work was much harder then and I was pushed away from it," he recalls.

But while he was studying economics and geography in London, Haward's father died and he returned to Mersea to help his mother keep the family trade going for a seventh generation.

It was a tough start. The "Great Freeze" of 1963 virtually wiped out the sensitive Colchester oysters and Haward mostly caught and sold fish in the early years. He gradually moved back to oysters as stocks recovered and he weathered parasite outbreaks along the way. In the 1980s his workaholic tendencies inadvertently sparked a successful offshoot business, his wife Heather's Company Shed seafood bar where tourists and locals queue out the door for a space around mismatched tables laden with lobsters, clams, fish and oysters.

Haward bought the disused little hut, realised he did not need it for oysters and hatched a plan to distract Heather from his antisocial hours. "I thought she could use it at weekends so she wouldn't moan at me for working. She started selling shellfish at the window and then people started sitting down and eating what they had bought," he recalls.

When financial disaster struck the family in the recession of the early 1990s, the shed and the oyster "layings" in his mother's name were all Haward had left.

"We'd borrowed a lot of money to expand, interest rates went through the roof, we couldn't cope and the company went into administration and we lost everything," says Haward.

But he cautiously built the business back up and it is now one of the biggest producers in the UK. Takings are now more evenly spread between different clients and Haward makes extra money by selling for other producers. He harvests 300,000 of his own oysters a year but sells four times that many.

Haward is 65 next month and three of his four children work in the business but retirement is out of the question. Next up is a further push to make the most of that growing domestic appetite.

"We have got to try and spread our business more widely still and one of the things is to sell directly to the consumers. Oysters are not an easy thing to sell. We really have to convince people to try them," he says.

So supermarkets are off the agenda. Getting new recruits to the oyster fold means wooing customers at places like London's Borough Market.

"I often say that if I ask 100 people do they like oysters 50 will say yes and 50 no and if the latter 50 are asked if they have tried them, probably less than half will say yes," explains Haward.

Exports are also a big opportunity and at the moment make up only 5% of his business.

With key producer France suffering low oyster harvests following several years of troubles with a herpes virus, the time is ripe for British cultivators.

Haward hopes trade with Dubai, in particular, will pick up as a result, while he is competing with the Dutch to grow market share in Belgium and also exporting to Singapore. But one country still eludes him: "I haven't yet been able to crack the Italian market but I think we might get in this year."

And so two millennia on from the Romans' initial love affair with Colchester Natives, the British delicacies may be finding their way to a new generation of Italians.